Conventionally, there are flow meter devices for measuring the flow rate of a fluid in piping by using a plurality of measurement passages connecting to the piping. One such known flow meter device is an ultrasonic flow meter device disclosed in Patent Literature 1. FIG. 10 shows such an ultrasonic flow meter device 100, which is configured as follows: a plurality of flow rate measurement units 101 are provided between an upstream chamber 102 and a downstream chamber 103; and an ultrasonic vibrator is disposed on each of the flow rate measurement units 101.